Aqueous stable lysine solution

ABSTRACT

Herein is disclosed an aqueous stable lysine solution containing an acid radical in such amount that the solubility of lysine therein has been increased than in the corresponding aqueous lysine base solution, whereby during storage of lysine in the form of a free-lysine solution (liquid composition), the precipitation of lysine base crystals due to the drop in temperature is prevented thereby improving the handling thereof during transportation (transfer) etc.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field to Which the Invention Belongs

[0002] The present invention relates to the stabilization of a lysinesolution, and in particular to the stabilization of a lysine solution byincorporating a predetermined amount of an acid radical therein.

[0003] Incidentally, the acid radical is the residue of an acid moleculefrom which one or more hydrogen atoms capable of being replaced bymetal(s) have been removed, and it constitutes the negative moiety of asalt. The acid radical often refers to an atomic group such as the acidradical (SO₄) of sulfuric acid, but a single atom such as Cl in hydrogenchloride is also referred to as an acid radical, this nomenclature beingfollowed in this specification.

[0004] Furthermore, the solubility of lysine refers to the equilibriummaximum amount of lysine soluble in unit water amount of a lysinesolution.

[0005] Still furthermore, the product of the molar number of an acidradical multiplied by its valence refers, e.g., to the molar number ofthe acid radical when the acid radical consists of a monovalent acidradical only, or to the product of the molar number of the acid radicalmultiplied by 2 as its valence when the acid radical consists of adivalent acid radical only, or to the sum of the molar number of amonovalent acid radical and the product of the molar number of adivalent acid radical multiplied by 2 as its valence when the acidradical consists of both monovalent and divalent acid radicals.

[0006] 2. Prior Art

[0007] As is well-known, lysine is used as one of the essential aminoacids in a large amount as a feed additive for producing a feed fordomestic animals such as cattle, pigs and chickens as well as anindustrially produced mixed feed. In so doing, however, lysine is notused as crystals in the free and pure form but used usually in the formof monohydrochloride, because lysine is readily soluble in water, ishardly crystallized in the free form, exhibits strong moistureabsorption (i.e., is strongly hygroscopic), absorbs carbon dioxide fromthe air, possesses a significantly unpleasant odor and is liable todegradation. In the present specification, lysine means lysine in theL-form (i.e. L-lysine) except quotations from the prior art literatureand is referred to as “lysine base” when it is intended to emphasizethat lysine is not in a salt form but in the free form (free lysine)

[0008] The monohydrochloride is a compound which is stable, not liableto degradation and readily crystallized, and does not possessesproperties such as moisture absorbing and unpleasantly smelling.However, its production involves the problems of additional raw materialcosts and process costs. Further, the use of lysine monohydrochloridefor enriching lysine in feeds and industrially produced mixed feedsincreases not only the content of lysine but also the content ofchlorides in the mixed feeds, but this is generally undesired. Further,the ratio of lysine to chlorides is also important. This is because, infeeding experiments with crystalline amino acid feeds, it is oftenobserved that the positive effects of the amino acid added arecompletely lost, when the amino acid is used as the hydrochloride,whereby the chloride excess, in turn, occurs. For these reasons, lysinein the chloride-free form has been strongly desired for the purpose ofnutritional enrichment for feeds and industrially produced mixed feeds.

[0009] Under such technical background, the JP-B 3-5783 patent documentdiscloses an invention titled “A process for producing a feed and anindustrially produced mixed feed enriched with lysine wherein an aqueousL-lysine solution containing 30 to 80 weight % L-lysine is used”.

[0010] With respect to the findings on which this prior art invention isbased, said document states, “It has been found that when L-lysine isused in the form of an aqueous solution for enrichment, L-lysine, whichis unstable in the free form, can be used for enrichment of feeds andmixed feeds. It has been unexpected that the aqueous solution is stableeven at high temperatures in storage for a long time. A comparativeexperiment has showed that an aqueous 70% L-lysine solution is notcolored at all after storage at 50° C. for 6 weeks. An experiment onby-products which may be formed depending on the condition has alsoindicated minus. As compared with the product in solution, crystallineL-lysine is evidently colored during this storage. Formation ofby-products has been confirmed in an analytical experiment. Accordingly,the found behavior described above has been absolutely unexpected,because general experience teaches that products liable to degradationare more easily degraded in a dissolved form than in a crystallineform”. The patent document makes comments on the advantages of theinvention, “An aqueous solution of lysine can be produced easily ascompared with crystalline L-lysine monohydrochloride, and the aqueoussolution has the advantage that the content of chlorides in mixed feedsis not increased and the solution can be accurately metered even in asmall amount. When a mixed feed is to be enriched with L-lysine, theL-lysine as a liquid composition does not usually require inevitableproduction of a pre-mixture having L-lysine at a correspondingly highconcentration. The aqueous solution of lysine can, directly at a desiredconcentration, be mixed uniformly with other ingredients previouslypresent at desired concentrations in a mixed feed, for example bysprinkling the lysine solution in a mixing cooker.” Concerning theunexpectedness of the invention, the document additionally states,“Although L-lysine is referred to as one kind of amino acid which isdestroyed first of all by heat treatment not only in materials but alsoin feeds and mixed feeds—this free L-lysine is added in the form of anaqueous L-lysine solution, and is unexpectedly stable even in feeds andmixed feeds. Degradation and/or reaction does not occur due to otherfeed ingredients. In a feeding experiment, an aqueous L-lysine solutionand L-lysine monohydrochloride exhibit the same action insofar as theseare used in the same molar amount”.

[0011] The patent document describes, concerning the concentration ofthe aqueous lysine solution of the invention disclosed therein, “Toachieve the desired improvement as to weight increase and utilization offeed, various amounts of L-lysine should be added to each mixed feed inorder to compensate for the content of natural L-lysine in feed protein.To use an aqueous L-lysine solution according to the present invention,the amount thereof is generally 0.01 to 5%, relative to the weight ofthe finished mixed feed, depending on the concentration of the L-lysinein the solution. In this case, a solution with a L-lysine content of 30to 80% by weight, advantageously 50 to 70% by weight, is particularlypreferable.”, and in respect of the process for producing the same, thedocument states, “Such a solution is obtained by dissolving L-lysine ina corresponding amount of water. In commercially producing L-lysine, itis naturally easy and suitable to produce an aqueous solution containingL-lysine at a desired concentration during the commercial production ofL-lysine. This evidently facilitates production and does not so cost asin production of particularly L-lysine monohydrochloride.”

[0012] For nutritionally enriching feeds or industrially produced mixedfeeds with lysine, lysine in the form of a liquid composition possessessuch various advantages as described in JP-B 3-5783 supra, but theliquid composition of lysine described in the patent document involvesthe problem that the lysine is easily precipitated as free form lysinecrystals as the temperature of the atmosphere drops during storage.Precipitation of such crystals will, in turn, cause clogging of pipesfor transferring the liquid composition of lysine in factories or duringshipping and unloading or make it difficult to transfer the liquidcomposition of lysine at a predetermined concentration, thus worseningthe handling of the liquid composition of lysine.

[0013] To sum up, when lysine is used in the form of a liquidcomposition, a lysine base solution has been used in many cases becauseof higher solubility than in a lysine salt solution such as lysinehydrochloride solution, lysine sulfate solution etc. However, from theconventional lysine base solution with a concentration of not less than50% by weight, as described in JP-B 3-5783 supra, lysine base iscrystalized when the temperature drops during storage, to cause, e.g.,clogging of piping, thus worsening the handling in some cases.

SUMMARY OF THE INVENTION

[0014] [Problems to Be Solved by the Invention]

[0015] Under the technical background described above, an object of thepresent invention is to provide a method wherein during storage oflysine in the form of a free-lysine solution (liquid composition), theprecipitation of lysine base crystals due to the drop in temperature isprevented thereby improving the handling thereof during transportation(transfer) etc. This object can be achieved after all by raising thesolubility of lysine in a lysine base solution, and thus the object ofthe present invention is, in other words, to provide a method ofimproving the solubility of lysine in an aqueous lysine solution thuspreventing precipitation of lysine crystals during storage andtransportation to improve its handling.

[0016] The raised solubility of lysine in a lysine solution leads toimprovement of the handling of the lysine solution (liquid composition)and the high-conc. lysine solution (high-conc. liquid composition) thusprovided, in turn, brings about the advantages that it contributes to areduction in the cost for transportation of lysine solutions or thatoperational costs can be reduced in spray-granulating by feeding ahigh-conc. solution.

[0017] [Means to Solve the Problems]

[0018] As a result of their eager study, the present inventors havefound that the acid radical of, e.g., hydrochloric acid (orhydrochloride) or sulfuric acid (or sulfate) is added at a predeterminedratio to the lysine, to an aqueous lysine base solution, whereby thesolubility of lysine can be raised than in the original aqueous lysinebase solution (as a matter of course, the comparison having beenconducted at a certain temperature), and on the basis of these findings,the present invention has been completed.

[0019] Accordingly, the present invention relates to an aqueous stablelysine solution containing an acid radical in such amount that thesolubility of lysine therein has been increased than in thecorresponding an aqueous lysine base solution, said correspondingaqueous lysine base solution meaning an aqueous lysine base solutionhaving the same composition as said aqueous stable lysine solution ofthe present inuention except with no acid radical contained therein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 shows the solubility curve at 20° C. of lysine depending onthe amount of hydrochloric acid relative to the lysine (Example 1).

DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, the present invention will be described in moredetail.

[0022] The aqueous stable lysine solution of the present invention(liquid lysine composition) is an aqueous lysine solution containing anacid radical at a predetermined ratio of the acid radical to the lysine.Incidentally, such a liquid lysine composition containing an acidradical at a predetermined ratio of the acid radical to the lysine is anovel material (novel composition). This is because the Japanese patentdocument supra refers to an aqueous lysine base solution only, withrespect to the process for producing the liquid lysine composition, asin: “Such a solution is obtained by dissolving L-lysine in acorresponding amount of water” as quoted above, and an aqueous lysinesolution containing an acid radical at the ratio specified according tothe present invention has not been known in any other prior artliteratures.

[0023] Further, it is not easy from the prior art to find an aqueouslysine base solution containing an acid radical at such ratio that thesolubility of lysine is higher at a certain temperature than in itscorresponding aqueous lysine base solution containing no such acidradical at the same temperature. As has been described above, lysinebase is readily soluble in water, while lysine monohydrochloride isreadily crystallized. It is reasonable therefrom to estimate that whenhydrochloric acid is gradually added to an aqueous lysine base solution,the solubility of lysine is gradually decreased as the concentration ofhydrochloric acid is increased, thus bringing about crystallization oflysine monohydrochloride, and it is difficult to estimate that thesolubility of lysine base is increased transiently during the course inwhich the ratio of hydrochloric acid is raised until lysinemonohydrochloride is crystallized, as found by the present inventors.

[0024] The aqueous stable lysine solution of the present invention canbe prepared very easily by those who are skilled in the art. This isbecause lysine base crystals or lysine salt crystals are dissolved at acertain temperature in a lysine base solution or in its correspondinglysine base solution containing an acid radical, and then the amount ofthe acid radical relative to the lysine in the solutions and thesolubility of lysine therein are measured, thereby plotting thesolubility curve of lysine depending on the amount of the acid radicalrelative to the lysine so that the desired amount (range) of the acidradical relative to the lysine can be easily determined.

[0025] Of course, the aqueous stable lysine solution of the presentinvention can be easily prepared by adding an acid radical to a lysinebase solution at a suitable ratio of the acid radical to the lysine, andthere are no limits thereto. Alternatively, the aqueous stable solutioncan be prepared by any of the following methods:

[0026] (1) A lysine-containing solution such as a lysine salt solutionor a mother liquor remaining after the lysine has been precipitated as asalt thereof from a lysine fermentation broth or a reaction mixtureresulting from lysine fermentation, lysine synthesis or proteinhydrolysis, is passed through a cation-exchange resin, whereby thelysine is adsorbed onto it. Thereafter, the adsorbed lysine is elutedwith, e.g., ammonia water or the like, and the eluate is concentratedwhile the ammonia is removed, to prepare a lysine base solution. Asuitable amount of an acid radical is added to this lysine basesolution, whereby the desired aqueous stable lysine solution can beprepared.

[0027] Here, the phrase “an acid radical is added” concretely meansaddition of a free acid such as hydrochloric acid or sulfuric acid, orits salt (sodium chloride, ammonium sulfate etc.). This is because thefree acid and its salt both contain an acid radical.

[0028] (2) Calcium hydroxide, barium hydroxide etc. are added to suchlysine-containing solution described above, whereby an excess sulfateradical contained therein is removed by precipitating it as sparinglysoluble salts such as barium sulfate until the acid radical has beenreduced to a predetermined level. Thus, the aqueous stable lysine basesolution can be obtained.

[0029] (3) The lysine-containing solution described above is passedthrough an OH-form anion-exchange resin so that the acid radical isremoved by adsorbing it onto the resin, whereby the aqueous stablelysine solution with a predetermined amount of the acid radical can beobtained. In this case, the acid radical may be removed until it isreduced to a predetermined level, and it is naturally not necessary toremove all the acid radical moiety.

[0030] (4) A lysine base solution obtained from the abovelysine-containing solution by the method described in (1) above is mixedwith a lysine salt solution such as a lysine hydrochloride solution, orwith an acid radical-containing solution resulting from fermentation orsynthesis, or with a mother liquor remaining after lysine hydrochloridecrystals has been crystallized, whereby the aqueous stable lysinesolution with a predetermined amount of the acid radical can beobtained.

[0031] The lysine stable solution of the present invention may containcations, proteins, organic acids etc. derived from a lysine fermentationbroth or a lysine synthetic mixture unless the effects of the presentinvention are deteriorated.

[0032] The thus obtained lysine base solution containing an acid radicalfrom an acid such as hydrochloric acid, sulfuric acid, or the like is anovel composition as described above and possesses the effects ofpreventing the precipitation of lysine base crystals at lowertemperatures during storage while providing a higher conc. solution.

[0033] Hereinafter, the foregoing will be described in more detail.

[0034]FIG. 1 shows the solubility curve of lysine at, e.g., 20° C.depending on the amount of the hydrochloric acid relative to the lysine,as measured by the present inventors (Example 1 infra). The solubility(g) of lysine per 100 g water is shown on the ordinate, while the molarratio (%), relative to the lysine, of the hydrochloric acid in thesolution is shown on the abscissa.

[0035] According to the findings of the present inventors, also at othertemperatures such as 30° C. or −20° C. and also with respect to otheracids such as sulfuric acid etc., the solubility of lysine is increasedin all the temperature range until a certain point in the molar ratio,while the molar ratio of an acid radical to the lysine is increased from0.

[0036] As can be seen from FIG. 1, an aqueous lysine base solutioncontaining lysine in an amount of the solubility at 20° C. but nohydrochloric acid (which is an aqueous saturated lysine solution)becomes supersaturated when the temperature is lowered to less than 20°C., to precipitate lysine base crystals. On the contrary, however, ifhydrochloric acid is contained in a predetermined range, even an aqueouslysine solution containing the same amount of lysine per unit wateramount of the solution at the same temperature hardly becomessupersaturated even if the temperature is lowered to some degree, thuspreventing precipitation of lysine crystals.

[0037] The aqueous stable lysine solution according to the presentinvention means an aqueous lysine solution from which, owing toincorporation of an acid radical at a predetermined ratio of the acidradical to the lysine, lysine crystals are hardly precipitated upon adrop in temperature as compared with a lysine base solution containingno acid radical (in order words, the solution is stabilized with respectto precipitation of lysine crystals upon a drop in temperature).

[0038] As can be seen also from FIG. 1, the lysine solution containinghydrochloric acid can contain, e.g., at 20° C. lysine at higherconcentrations per unit amount of water (e.g., weight) than in thecorresponding lysine base solution containing no hydrochloric acid.

[0039] In the aqueous stable lysine solution containing an acid radical,from which lysine base crystals are hardly precipitated upon temperaturechange (−30 to 80° C.) in a practical atmosphere, the content of theacid radical is preferably 35% or less, more preferably in the range of1 to 27%, and still more preferably in the range of 5 to 25%, in termsof the ratio of the product of the molar number of the acid radicalmultiplied by the valence of the acid radical to the molar number oflysine.

[0040] The acid radical is preferably the chloride radical, the sulfateradical or a mixture thereof. As described above, the chloride radicalincludes the one derived from hydrochloric acid or salts such as sodiumchloride, potassium chloride and ammonium chloride, and the sulfateradical includes the one derived from salts such as sodium sulfate,sodium hydrogen sulfate, potassium sulfate and ammonium sulfate. If theacid radical is the chloride radical, the content thereof is preferably35% or less, more preferably in the range of 1 to 27%, and still morepreferably in the range of 5 to 25%, in terms of the ratio of the molarnumber of the chloride radical to the molar number of the lysine. If theacid radical is the sulfate radical, the content thereof is preferably17% or less, more preferably in the range of 2 to 13%, and still morepreferably in the range of 6 to 13%, in terms of the ratio of the molarnumber of the sulfate radical to the molar number of the lysine. If theacid radical is a mixture of the chloride radical and the sulfateradical, the content of the mixture is preferably 35% or less, morepreferably in the range of 1 to 27%, and still more preferably in therange of 5 to 25%, in terms of the ratio of the sum of the molar numberof the chloride radical and the product of the molar number of thesulfate radical multiplied by 2 as its valence to the molar number ofthe lysine.

[0041] There are no particular difficulting in a process per se forproducing a lysine-enriched feed or an industrially produced mixed feedby the use of the aqueous stable lysine solution of the presentinvention, and conventional known techniques using lysine in the form ofa liquid composition, for example, the techniques described in JP-B3-5783 supra can be used. That is, the desired feed can be produced inthe same manner as described in the patent document supra except thatthe aqueous stable lysine solution of the present invention is used inplace of the “aqueous L-lysine solution” referred to therein.

EXAMPLES

[0042] The present invention will be described in more detail byreference to the Examples.

Example 1

[0043] (1) 1,015 g of medical grade lysine hydrochloride anhydridecrystals were dissolved in 5,000 g of deionized water and the mixturewas adjusted to pH 3.0 with reagent grade 35% hydrochloric acid. Thesolution was passed at a flow rate of 19 L/hr through a column packedwith 19 L of NH⁺-form cation-exchange resin (“Diaion SK-1B”, exMitsubishi Chemical Industries Ltd.), whereby the lysine was adsorbedonto the cation-exchange resin. After adsorption, the column was washedby passing 38 L of deionized water therethrough at the same flow rate of19 L/hr, and after 38 L of 2 N ammonia water was passed through thecolumn at the same flow rate of 19 L/hr, 38 L of deionized water waspassed therethrough at the same rate of 19 L/hr, whereby the lysine waseluted. 76 L of this eluted lysine solution was concentrated underreduced pressure (50 mmHg) until the lysine concentration reached 70%,whereby a lysine base solution was obtained. These procedures wererepeated 5 times, whereby 4,600 g of aqueous 70% lysine solution wasobtained.

[0044] (2) A 1,800 g portion of the lysine base solution with a lysineconcentration of 70% obtained under (1) above was stirred under coolingat a rate of −10° C./hr from 50° C. to 10° C. so that lysine basecrystals were precipitated. The crystals were separated and air-dried,whereby 500 g of lysine base crystals were obtained.

[0045] (3) 390 g of medical grade lysine hydrochloride anhydridecrystals were introduced into 300 g of deionized water and dissolved byraising the temperature to 60° C. in a water bath. The solution wasstirred under cooling to 15° C. at a rate of −10° C./hr, whereby lysinehydrochloride. 2H₂O crystals were precipitated. The crystals wereseparated and air-dried to give 280 g of lysine hydrochloride.2H₂Ocrystals.

[0046] 70% lysine base solution obtained under (1) above, 35%hydrochloric acid and deionized water were used in the amounts shown inTable 1 below, respectively, to prepare 7 kinds of solutions. In thesesolutions, the lysine base crystals obtained under (2) above and thelysine hydrochloride.2H₂O crystals obtained under (3) above weresuspended respectively in the amounts shown in the same table, and thenstirred for 1 week during which the temperature was kept at 20° C.

[0047] The crystals were removed from these suspensions, and theconcentration of the chloride ions in each of the remaining solutionswas analyzed by an ion chromatographic analyzer “Yokokawa IC7000 model”,and the concentration of lysine therein was analyzed by an amino acidanalyzer “Hitachi L-8500 model”. The results are also shown in FIG. 1below. TABLE 1 Experimental Conditions 35% lysine Operation 70% lysinehydrochloric deionized water lysine base hydrochloride No. solution (g)acid (g) (g) crystals (g) crystals (g) 1 350  0 58 40 2 377 22 46 106 3378 38 32 155 4 365 52 42 147 4.2 5 326 28 41 49 54 6 401 52 42 1.6 19 7397 68 38 1.8 22

[0048] As can be seen from FIG. 1, the solubility of lysine is increasedwhen the chloride ions (the chloride radical) are contained at a molarratio of 27% or less to the lysine, as compared with the case where thechloride ions are not contained.

Example 2

[0049] Lysine base crystals obtained in the same manner as in Example1(2), lysine hydrochloride.2H₂O crystals obtained in the same manner asin Example 1(3) and deionized water were used respectively in theamounts shown in Table 2 below to prepare 5 kinds of suspensions, andeach suspension was stirred for 1 week during which the temperature waskept at 30° C. or −20° C.

[0050] The crystals were removed from these suspensions, and theconcentration of the chloride ions in each of the resulting solutions(supernatants) was analyzed by the ion chromatographic analyzer“Yokokawa IC7000 model”, and the concentration of the lysine therein wasanalyzed by the amino acid analyzer “Hitachi L-8500 model”. The resultsare also shown in the same table. TABLE 2 Experimental Condition Resultsof Analysis of Supernatant Components Operation lysine hydrochloridelysine base crystals temperature Chloride ion solubility of lysineHCl/Lys No. deionized water (g) crystals (g) (g) (° C.) concentration(wt %) (g/100 g-H₂O) (molar ratio) 1 40 0 95 30 0 160 0% 2 37 30 80 303.4 175 22.8% 3 36 35 80 30 3.9 179 26.0% 4 37 45 58 30 5.0 160 35.0% 544 0 60 −20 0 102 0% 6 43 8 55 −20 1.4 106 11.5%

[0051] As can be seen from the table, the solubility of lysine isincreased too at varied temperatures by incorporating chloride ions(i.e., chloride radical).

Example 3

[0052] 300 g of 60% lysine base solution obtained in the same manner asin Example 1(1) was placed in a water bath and 63.5 g of reagent grade95% sulfuric acid was gradually added thereto. After addition ofsulfuric acid was finished, the mixture was kept at a temperature of 50°C. and then stirred under cooling from that temperature to 10° C. at arate of −10° C./hr, to precipitate lysine sulfate crystals. The crystalswere separated and air-dried to give 90 g of lysine sulfate crystals.The lysine sulfate crystals, lysine base crystals obtained in the samemanner as in Example 1(2) and deionized water were used respectively inthe amounts shown in Table 3 below to prepare suspensions, and eachsuspension was stirred for 1 week during which the temperature was keptat 20° C. The crystals were removed from these suspensions, and theconcentration of the sulfate ions in each of the resulting solutions(supernatants) was analyzed by the ion chromatographic analyzer“Yokokawa IC7000 model”, and the concentration of the lysine therein wasanalyzed by the amino acid analyzer “Hitachi L-8500 model”. The resultsare also shown in the same table. TABLE 3 Results of Analysis ofSupernatant Experimental Conditions Components Operation deionizedlysine sulfate lysine base sulfate ion solubility of lysine No. water(g) crystals (g) crystals (g) concentration (wt %) (g/100 g-H₂O) 1 41  090 0 147 2 41 10 85 1.9 158 3 42 20 75 2.8 157

[0053] From the table, the effect of increasing the solubility of lysineby incorporating sulfate ions (SO₄ ²⁻, sulfate radical) is recognizedsimilarly to the case where chloride ions (Cl⁻, chloride radical) areincorporated.

Example 4

[0054] A lysine base solution with a lysine concentration adjusted to62% was prepared by adding 26.8 g of 35% hydrochloric acid to 241 glysine base solution with a lysine concentration of 74.3% obtained inthe similar manner as in Example 1(1) and then adding 22 g of deionizedwater thereto, and another lysine base solution with a lysineconcentration adjusted to 62% was prepared by adding 48 g of deionizedwater to 239 g lysine base solution with a lysine concentration of74.3%. The resulting solutions, that is, the lysine base solutioncontaining hydrochloric acid and the lysine base solution containing nohydrochloric acid were stirred, respectively, in sealed vessels in athermostatic bath at 20° C.

[0055] After 8 days, comparison of both solutions revealed that lysinebase crystals had been precipitated in the system where hydrochloricacid was not added, whereas precipitation of crystals was not observedin the system where hydrochloric acid was added. Accordingly, thestability of the lysine base solution with respect to precipitation ofcrystals can be improved by incorporating hydrochloric acid (chlorideions).

Example 5

[0056] A lysine base solution with a lysine concentration of 75.6%obtained in the similar manner as in Example 1(1), aqueous 25% sodiumchloride solution, aqueous 25% ammonium chloride solution and deionizedwater were used respectively in the amounts shown in Table 4 below, toprepare 2 kinds of solutions. Lysine base crystals obtained in the samemanner as in Example 1(2) were suspended in these solutions in theamounts shown in the same table, and stirred for 1 week during which thetemperature was kept at 20° C.

[0057] The crystals were removed from these suspensions, and theconcentration of the chloride ions in each of the resulting solutions(supernatants) was analyzed by the ion chromatographic analyzer“Yokokawa IC7000 model”, and the concentration of the lysine therein wasanalyzed by the amino acid analyzer “Hitachi L-8500 model”. The resultsare also shown in the same table. TABLE 4 Result of Analysis ofExperimental Conditions Supernatant Components 75.6% lysine 25% NaCl 25%NH₄Cl deionized lysine base Chloride ion Solubility of Operationsolution solution solution water crystals concentration lysine No. (g)(g) (g) (g) (g) (wt %) (g/100 g-H₂O) 1 151 36 10 16 3.1 164 2 122 27 113.3 178

[0058] [Effects of the Invention]

[0059] According to the present invention, a free acid such ashydrochloric acid or sulfuric acid, or a lysine salt such as lysinehydrochloride or lysine sulfate is added to a lysine base solution at apredetermined ratio of the acid radical to the lysine in the solution,whereby the concentration of lysine can be made higher than in asolution of lysine base alone. That is, addition of an acid radical inthese forms can make the lysine base solution stable at higherconcentration, whereby even the lysine base solution can be storedwithout undergoing the precipitation of lysine base crystals due to,e.g., a drop in temperature, the cost for transportation of lysinesolutions can be reduced, and in the case where the lysine solution issubjected to spray-granulation, the high-conc. solution can be sprayed.

[0060] Briefly, the solubility of lysine in water can be improved (i.e.,increased) according to the present invention thereby preventing theprecipitation of crystals upon a drop in temperature, and the stablelysine solution can be easily prepared at a higher concentration, thusimproving the handling of the lysine solution during transportation etc.What is claimed as new and desired to be secured by Letters Patent is:

1. An aqueous stable lysine solution containing an acid radical in suchamount that the solubility of lysine therein has been increased than inthe corresponding aqueous lysine base solution.
 2. The aqueous stablelysine solution as set forth in claim 1, wherein the content of the acidradical is 35% or less, in terms of the ratio of the product of themolar number of the acid radical multiplied by its valence to the molarnumber of the lysine.
 3. The aqueous stable lysine solution as set forthin claim 1 or 2, wherein said acid radical is the chloride radical (Cl⁻)and/or the sulfate radical (SO₄ ²⁻).
 4. The aqueous stable lysinesolution as set forth in claim 1, wherein said acid radical is thechloride radical (Cl⁻) and is contained within the range of 35% or lessin terms of the molar ratio thereof to the lysine.
 5. The aqueous stablelysine solution as set forth in claim 1, wherein said acid radical isthe sulfate radical (SO₄ ²⁻) and is contained within the range of 17% orless in terms of the molar ratio thereof to the lysine.
 6. Alysine-enriched feed and an industrially produced mixed feed wherein theaqueous stable lysine solution described in any one of claims 1 to 5 hasbeen used.